The project will be concerned with the development of a technique which will allow analysis of the chromosome constitution of human spermatozoa. In vitro insemination of zona-free hamster eggs with human sperm will be used to reactivate the sperm nucleus to the state where their chromosomes are individually visible prior to the fusion of male and female pronuclei. At this stage, the chromosomes will be analyzed using standard cytological procedures. The aim of the project is to determine by direct observation the types and frequencies of chromosome aberrations in human spermatozoa in normal, healthy males of different ages and to examine the chromosome constitution of the gametes of male individuals with balanced chromosome rearrangements.